It is known to produce a shaped synthetic-resin extrusion by continuously ejecting a hot synthetic-resin strand in plastic condition from an extrusion molder or the like and pulling this preshaped strand through a calibrating dye and a cooling bath. The hot strand is accurately shaped by the calibrating dye and is then hardened into this shape as it passed through the cooling bath.
A synthetic-resin extruder generally produces a relatively constant volume/time output rate and the pulling arrangement, in the form of two wheels or two juxtaposed belts that grip the hardened and calibrated strand, usually operates at a relatively constant distance/time rate. Thus when the machine is started a skilled worker sets the extruder and pulling device such that a small mass or bank of material is left immediately upstream of the calibrating die to compensate for slight fluctuations.
In such arrangements it is necessary that a highly skilled worker constantly survey and readjust the machine. Otherwise the bank upstream of the calibrating die might grow too large and allow the synthetic-resin strands to cool excessively before entering this die. Alternatively it is possible that the extrusion rate will decrease somewhat and/or the pulling rate will decrease somewhat and/or the pulling rate will increase so that the bank will be eliminated and the strand will become too thin to calibrate properly.
Another difficulty with such a system is that it is very difficult to apply to an arrangement which is intended to produce C-, T-, U-, and I-shaped extrusions. Furthermore, when a thermosetting resin is employed there is the danger that the material will set in the bank so much that it will no longer be plastic and will therefore be impossible to calibrate with any precision. Thus it is frequently necessary to shut down the apparatus and throw out the strand in production in order to readjust the arrangement and start production again.